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Certain high reeds 'consume' more air than others


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I tried digging around for answers to this but couldn't come up with anything, so here we are. 

 

Ive been thinking about this a lot lately as my trad playing requires ever bit of air in the bellows to be efficiently used, so when there's a problem its usually quite noticeable.

 

 Ive noticed for a while now that the speed at which my bellows will close changes depending on the reeds, and while that would make logical sense between low reeds and high reeds (lows using more air to cycle, highs less) the most surprising and frustrating rate is that of the D''' (right hand, first row, third button push). The neighboring push reeds consume at a pretty consistent rate for what you'd expect, but for some odd reason that D''' and maybe the neighboring G''' cause the bellows to close at an alarming rate comparatively. 

 

Additionally confusing is the fact that the reed set is pretty good, volume balance and intializing/swing cycle speed are all pretty consistent with the rest, but I cannot for the life of me figure it out, so im ordering a few other reeds in to see if there's a difference.

 

The fact that they're not valved makes me wonder, but ive not run into this issue before with non-valved reeds. I imagined that if a reed cycled at the appropriate rate (which it would need to in order to produce the desired pitch, no?) Perhaps there would be air loss, but I cant come up with enough logic in that concept to buy it. 

I feel like I'd read something about this in the past but I simply cant recall.

 

I'll see if I can slap a video together soon for reference.

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I can't claim expertise on this topic, but I have spent enough time tweaking reeds on enough instruments that I may be able to add something..

 

Clarification questions: is this english, anglo, hybrid, etc?

 

Valves: The no valves thing raises a red flag in my mind. If other reeds behaving well at similar pitch are valved, but the opposing reeds on the inefficient buttons are not valved, that could be a factor. My understanding (and would love for others to fill me in if this is an incomplete understanding) is that the highest reeds don't need valves because they are unlikely to start vibrating when air is coming from the wrong direction on the shoe side, and the leakage is small because the reed is small and stiff. So to confirm, are the opposite reeds (push vs pull) unvalved on the inefficient D''' and G''' notes? Valves being cheap, it may be worth trying to valve those to see if it solved the problem before other more dramatic undertakings.

 

Tolerance (another sources of inefficiency): Again, I would love to hear from others, but in my limited experience, reeds that have a larger gap or lower tolerance tend to be inefficient, That makes complete sense to me. As the reed tongue end passes the top of the reed shoe, if there is a gap between the sides or the end that allows air to pass, more air passes without being converted to pressure variations (sound waves). If the reed is perfectly matched to the reed shoe, the reed is more efficient. This sort of 'leaking' could be due to a gap on the sides, or a gap at the end, or a tongue is shaped such that the end and sides pass the top of the reed shoe at different times (think of a curved reed). That might do interesting and possibly good) things to the voice of the reed, but would likely reduce efficiency.

 

There is a downside to high tolerance: The highest tolerance reeds I have encountered are on my wife Kara's Dipper, and they have extremely tight tolerance and are extremely efficient. But this Dipper suffers more with environment changes. Any change in humidity (and we keep all the instruments as close to 50% as we can in the winter using plastic bins) tends to lead to buzzing reeds and other problems. My guess is this is because the slight swelling or shrinking of reed pans changes the pressure on the reed shoe and the tolerance is so tight that even a small change leads to interference on these high tolerance reeds.

 

The last thing I can think of is if there is simply a leak on these reeds because the reed show is now well seated in the reed pan. It may be worth confirming that the reeds are comparably tight in the reed pan compared to the others that seem more efficient.

 

Best,

JDR

 

 

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JDR covered most of it. If the opposite reed in the chamber doesn't have a valve, it can definitely leak a bit causing increased air consumption, though I wouldn't normally call it "an alarming rate". You could try to narrow down the cause by temporarily blocking off the opposite reed by putting a bit of masking tape over where its valve would go.

 

If you're talking about a traditionally constructed instrument, the other thing to check for is leaks past the chamois gaskets around the affected chamber(s). This can be caused by wood shrinkage causing a gap to open up, flattened gasket material, or failed support blocks under the reed pan.

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It would really help if you'd tell us what make/model of concertina you're talking about @Oberon and (better still) provide photos of the offending reeds and how they're mounted, because not all concertinas/reeds are the same and the best answer is going to be different accordingly.

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Of course it might not be the reed that is losing air.  Their might be an air leak from the reed chamber by another route.  Where that could be depends on the construction of the concertina, so you would need to first answer the question above from Stephen Chambers before we could suggest where to look.  .

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